Recent developments of lightweight electronic devices have enabled users to take electronic devices with a display, such as mobile phones and personal computers, out of home and use in public places. A problem arises here that people near the user can view confidential documents and information meant for private browsing.
To address the problem, a display device is being proposed which normally operates in wide viewing angle display mode and when used in public places, can be switched to narrow viewing angle display mode. In the narrow viewing angle mode, the user, who is right in front of the display device, can view a normal display, but other people who are in oblique directions can see only a solid color or another image. Also, the capability to switch to the wide viewing angle display mode enables many people to view a captured image together or otherwise enables the user to use the device in situations where the wide viewing angle is needed.
A component realizing such a display is disclosed in Japanese Unexamined Patent Publication 9-105958/1997 (Tokukaihei 9-105958; published Apr. 22, 1997), for example. The viewing angle varying element disclosed there includes a liquid crystal layer between a pair of substrates. The element achieves the narrow viewing angle mode by aligning liquid crystal molecules vertical to the substrates and achieves the wide viewing angle by aligning them parallel to the substrates. Another component is disclosed in Japanese Unexamined Patent Publication 2004-62094 (Tokukai 2004-62094; published Feb. 26, 2004). The disclosed viewing angle varying means varies alignment of liquid crystal between two glass plates to change the viewing angle of information display means.
There are also display devices divided into some sections which differ, for example, in the direction of alignment of liquid crystal. This particular structure enables a narrow viewing angle mode in which observers who are not in front of the display device will see a different image from the one perceived by a user in front of the display device. For example, Japanese Unexamined Patent Publication 2001-264768 (Tokukai 2001-264768; published Sep. 26, 2001) discloses a liquid crystal display device containing aligning films which sandwich a liquid crystal layer are divided into multiple regions, the alignment direction differing between adjacent regions. In addition, Japanese Unexamined Patent Publication 2004-38035 (Tokukai 2004-38035; published Feb. 5, 2004) discloses a liquid crystal display device containing first liquid crystal cells and second liquid crystal cells having different viewing angle directions, the first and second liquid crystal cells being arranged alternately.
The Tokukaihei 9-105958 structure realizes the narrow viewing angle mode by vertically aligning liquid crystal molecules to change the refractive index. It is however difficult to retain image display quality with control of viewing angle through the refractive index.
Tokukai 2004-62094 does describe the control of the viewing angle of the display device through changes in liquid crystal alignment. The document however does not give any description on how to change the liquid crystal alignment, failing to realize the viewing angle control.
The Tokukai 2001-264768 structure is described to show a fixed pattern, no matter what the display signal, to observers who are not in front of the display device. Structurally, however, the display image cannot be hidden well from those observers who are not in front of the display device because the pattern appears reversed in gray levels when viewed from the right and from the left. Specifically, if the structure contains many regions which are non-transmissive when viewed from the right, many regions are transmissive when viewed from the left. So, the screen can be hidden from both the left and right sides only by superimposing an image, like hound's tooth checks, which consists of the same number of transmissive and non-transmissive regions.
The Tokukai 2004-38035 structure contains many small liquid crystal cells arranged on a plate. The liquid crystal display device involves a complex structure and difficult to manufacture.
As described in the foregoing, no known display device has high display quality, is capable of switching to a mode in which the display image is appropriately hidden when viewed from an oblique direction, and has a simple structure.